Testing the waters for text/troff

I am quite surprised that there is no registered MIME media type for text with nroff/troff markup, especially as that format has traditionally been used for RFC and Internet Draft documents (RFC 2223). I could find no record in the archives of this mailing list of any discussion on the matter. Has there been any proposal for such a text subtype, and if so, what were the reasons that have prevented it from being approved?